Apparatus for the electrical production of hydrogen

ABSTRACT

An apparatus for the electrical production of hydrogen from water includes an electrolyzer ( 1 ) of the PEM type. The electrolyzer ( 1 ) has an inlet ( 2 ) for the introduction of water and a first outlet ( 3 ) for the hydrogen which is enriched with water and/or water vapor and is produced in the electrolyzer ( 1 ) and also a second outlet ( 4 ) for oxygen. A water separation device ( 7 ) which has at least a thermal separation stage ( 10 ) adjoins the electrolyzer ( 1 ).

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a United States National Phase application ofInternational Application PCT/EP2011/001899 and claims the benefit ofpriority under 35 U.S.C. §119 of European Patent Application EP 10004114.4-1227 filed Apr. 19, 2010, the entire contents of which areincorporated herein by reference.

FIELD OF THE INVENTION

The present invention pertains to an apparatus for the electricalproduction of hydrogen from water.

BACKGROUND OF THE INVENTION

The use of electrolyzers for producing hydrogen from water by means ofelectric energy belongs to the state of the art. Such electrolyzersexist in various designs. The present invention pertains to an apparatuswith an electrolyzer of the PEM type (Polymer Electrolyte membrane),i.e., an electrolyzer that operates with a proton-permeable polymermembrane. Such electrolyzers are typically built in so-called stacks inorder to achieve the highest possible gas yield in the smallest possiblespace. Water is fed on one side here to each membrane, and splittinginto hydrogen and oxygen takes place by the electrodes, which arearranged on both sides of the membrane and are supplied with theelectrolysis voltage, and hydrogen is produced on one side of themembrane and oxygen on the other side, on which the water is fed.

To guarantee the permeability to protons of the polymer electrolytemembrane, it is necessary to keep the membrane moist at all times, whichdoes, however, cause the hydrogen produced to be also typically providedwith water vapor and/or water in the form of droplets. This water burdenbeing entrained in the hydrogen is undesired in many industrialapplications, and it is therefore to be removed. For example, the waterburden being entrained is thus to be removed before storage in case ofstorage of the hydrogen in the metal hydride storage means commonly usednow. Mechanical water separators are usually insufficient here, becausethey are unable to sufficiently free the hydrogen stream of water.

Arranging a water separation device, which operates according to theprinciple of pressure swing adsorption, downstream of the electrolyzeron the outlet side for drying the hydrogen therefore belongs to thestate of the art. The hydrogen stream, which leaves the electrolyzer andis enriched with water and water vapor, is sent now via one or moremolecular sieve beds, which bind the water. However, such binding takesplace only as long as the molecular sieve beds are not saturated. Themolecular sieve beds must therefore be regenerated at regular intervals.Two molecular sieve beds are therefore provided in practice, and flowtakes place through them alternatingly, and the non-active bed is beingregenerated by being flushed with dried hydrogen in counterflow. Thismethod is comparatively complicated and impairs especially theefficiency of the apparatus, because the hydrogen used for the backwashusually escapes unused. The method reaches its limits especially withincreasing water load in the hydrogen stream, and these apparatuses,which are known from the state of the art, are therefore ratherineffective.

SUMMARY OF THE INVENTION

Against this background, a basic object of the present invention is toprovide an apparatus of this type for the electrical production ofhydrogen from water such that it operates with the highest possibleefficiency for generated dried hydrogen, i.e., hydrogen freed of amajority of the water.

The apparatus according to the present invention for the electricalproduction of hydrogen from water has an electrolyzer of the PEM type,i.e., one that operates with a proton-permeable polymer membrane. Thiselectrolyzer is provided with an inlet for introducing water and with afirst outlet for the hydrogen, which is enriched with water and/or watervapor and is produced in the electrolyzer, as well as with a secondoutlet for oxygen and water. The apparatus has, moreover, a waterseparation device, whose inlet is connected by a line with the firstoutlet of the electrolyzer and whose gas-carrying outlet leads to ahydrogen removal port in or at the apparatus, wherein the waterseparation device has at least one thermal separation stage.

Thus, the basic idea of the present invention is to provide anelectrolyzer with water separation device within the apparatus, whereinthe water separation device has at least one first thermal separationstage. It is apparent that a mechanical separation apparatus may beprovided as a separator, for example, a cyclone separator or agravitational separator, in principle, as part of the separationapparatus or arranged upstream of the latter. Such a separationapparatus is not a separation stage in the sense of the presentinvention. The water separation device is typically of a two- or morethan two-stage design, the first stage being a thermal separation stage,in which water is removed from the hydrogen stream by cooling.

A hydrogen removal port in the sense of the present invention is definednot only as a port in the actual sense of the word but also as a linewithin or outside the apparatus, which sends the dried hydrogen to auser or to a storage means. Thus, such a hydrogen removal port in theapparatus can send hydrogen to a metal hydride storage means likewiseprovided in the apparatus via a line.

The solution according to the present invention is especiallyadvantageous because the electrolyzer can be operated at comparativelyhigh temperature and hence with high efficiency. The gas lossesoccurring during pressure swing adsorption are completely avoided.

Since the temperature should be as high as possible for effectiveoperation of the electrolyzer, but, on the other hand, the protonexchange membrane must always be kept wet, favorable operatingconditions are obtained in terms of efficiency if the electrolyzer isoperated in ranges of 70° C. to 80° C. or higher. The operatingtemperature is limited upwardly by the boiling point of water, whichmust not be reached under any circumstances. However, the water loadbeing entrained doubles with every 11° C. or so. Consequently, if theoperating temperature is increased from 60° C. to 70° C., the quantityof water to be removed approximately doubles. Such a quantity of wateris unproblematic with the solution according to the present invention,namely, with a first thermal separation stage, especially entirelywithout loss of hydrogen. The electrolyzer of the apparatus according tothe present invention can thus be operated substantially moreeffectively, because it is operated at a higher temperature, withouthaving to accept the losses known from pressure swing adsorption. Bycontrast, the energy to be used for cooling is markedly lower.

The water is advantageously separated in two stages, but more than twostages may be provided as well. The second separation stage isadvantageously likewise a thermal separation stage. As an alternative,the second separation stage may also be formed by a pressure swingadsorption apparatus. A pressure swing adsorption apparatus isconsidered for use as the second stage because only a small quantity ofwater is to be removed from the hydrogen here, but it is important toremove the water as completely as possible. Since the hydrogen is loadedwith small quantities of water only, the molecular sieve beds can beused for a comparatively long time before backwash is necessary.

According to a variant of the present invention, a water-carrying outletof at least the first separation stage is advantageously connected tothe inlet of the electrolyzer by means of a line for returning thewater. The connection by means of a line is brought about at least fromtime to time, i.e., corresponding valves, which can be actuatedcorrespondingly as needed in order to return the water collected in thefirst thermal separation stage to the inlet of the electrolyzer, areprovided in the line. The line pressure occurring in the system withinthe apparatus, i.e., the hydrogen pressure, can be used to transportthis water. A bypass line with valve is advantageously to be providedfor this, namely, between the first outlet of the electrolyzer, i.e.,the hydrogen-carrying outlet, and the separator to be emptied, bypassingthe separator or separators located in between.

An inlet of the electrolyzer is defined in the sense of the presentinvention as any water-carrying line leading thereto, which is fed, forexample, from a reservoir within or outside the apparatus. This watercan consequently be returned either into this line or advantageouslyinto the reservoir.

A mechanical preseparator, for example, a gravitational water separatoror a cyclone type water separator, is advantageously arranged betweenthe electrolyzer and the first thermal separation stage. Part of thewater load being entrained can be separated nearly without loss in sucha preseparator. It is especially advantageous in this connection tointegrate the preseparator in terms of the lines such that it can alsobe used at the same time to receive the water returned from theseparation stages. The preseparator can be advantageously shut off forthis both on the inlet side and the outlet side of its gas-carryinglines by means of valves and can be bypassed via a bypass line, whichcan likewise be shut off by means of a valve. When the return lines ofthe separation stages, which can likewise be shut off by means ofvalves, open again into the preseparator, the water to be returned canbe pressed by means of the pressure present anyway in the hydrogen lineinto the preseparator by shutting off the gas-carrying lines of thepreseparator and opening the bypass line when the valves in the returnlines are opened. It is unproblematic here if the gas enters thepreseparator in the form of hydrogen through the return lines, becausethis gas can again be fed later into the separation stages.

The preseparator likewise has a return line, which can be shut off bymeans of a valve and via which the water collected in the preseparatorcan be fed to the inlet of the electrolyzer or to the water tankarranged upstream of it. By using a float valve at the bottom of thepreseparator, the return of the water can take place quasi automaticallyinsofar as the shut-off valve in the return line leading to the watertank is opened.

The thermal separation stage or thermal separation stages is/areadvantageously provided with an electrically operated, common coolingapparatus. Such cooling apparatuses are available relativelycost-effectively and in a compact form. A compressor type coolingapparatus is advantageously used in case of larger apparatuses. Anabsorber cooling device or a cooling device operating with Peltierelements may also be used as an alternative, especially in case ofsmaller apparatuses. It is especially advantageous if the firstthermally operating separation stage is designed such that the hydrogenarriving from the electrolyzer that is enriched with water and/or watervapor is cooled to a temperature just slightly above the freezing point,i.e., preferably between 0° C. and 5° C. A majority of the water beingentrained in the hydrogen stream condenses in this temperature range.The residual water load in the hydrogen is comparatively small. Sincecooling takes place above the freezing point, no special precautionarymeasures are to be taken in respect to ice formation concerning theremoval of the condensed water.

Cooling to below 0° C. and preferably to below −35° C. advantageouslytakes place only in the second separation stage of the hydrogen stream.The water being entrained in the hydrogen is crystallized in the form ofice, typically on the heat exchanger walls, in this temperature range.These walls must therefore be deiced from time to time, which can beguaranteed by intermittent operation. Since such apparatuses are neveroperated typically for longer than 12 hours at a stretch, it is notusually necessary to interrupt the operation in case of suitable designof the cooling surfaces for the purpose of deicing, and it issufficient, instead, for the apparatus to thaw by itself after beingswitched off during the pause between operations, for example, duringthe night. If, by contrast, the apparatus is to be designed for a quasicontinuous, 24-hour operation, it is either necessary to provide for athawing cycle for the second thermal separation stage, which mayoptionally be supported by an electric heater, or to provide two thermalseparation stages in parallel operation, which are operatedalternatingly.

The apparatus according to the present invention operates especiallyeffectively if the electrolyzer, the water separation device as well asany auxiliary units, connection lines, valves and the like that may bepresent are designed such that the hydrogen is generated and maintainedunder a pressure of 20 bar or higher, preferably about 30 bar. Operationof the apparatus with this pressure is especially advantageous becauseno special pressure increase is necessary in this case for storing thehydrogen in metal hydride storage means. The apparatus releases the dryhydrogen with the necessary pressure.

The present invention will be explained in more detail below on thebasis of the exemplary embodiment shown in the drawings. The variousfeatures of novelty which characterize the invention are pointed outwith particularity in the claims annexed to and forming a part of thisdisclosure. For a better understanding of the invention, its operatingadvantages and specific objects attained by its uses, reference is madeto the accompanying drawings and descriptive matter in which preferredembodiments of the invention are illustrated.

BRIEF DESCRIPTION OF THE DRAWINGS

The only FIGURE shows a diagram of an embodiment variant of theapparatus according to the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to the drawings in particular, the apparatus shown in theFIGURE is arranged in an essentially closed housing, not shown, but itdoes not necessarily have to be so designed, but, especially if it isintegrated in an instillation, its components may be integrated in theinstillation.

The apparatus has an electrolyzer 1 of the PEM type, which is usuallydesigned as a stack, but it may be designed in any other suitable formas well. The electrolyzer has an inlet 2 for the introduction of water.A first outlet 3 of the electrolyzer 1 is provided for removing thehydrogen produced in electrolyzer 1, which typically contains water andwater vapor. Furthermore, electrolyzer 1 has a second outlet 4, which isprovided for removing the oxygen formed in electrolyzer 1.

In the embodiment shown, the apparatus has a reservoir 5 in the form ofa water tank, which is connected to the inlet 2 of the electrolyzer viaa pump 6 by means of a water line. The second outlet 4 opens via a linein the upper area of the water tank 5. The first outlet 3, i.e., thewater-carrying outlet 3, of electrolyzer 1 is connected by means of aline to a water separation device 7.

The water separation device 7 has a gravitational water separator 8,whose gas-carrying line 9 with connected to a first thermal separationstage 10 by means of a line. In this first thermal separation stage 10,which is formed from a closed container 11 with a coolant line 12integrated therein, the water-containing hydrogen stream arriving fromthe gravitational water separator 8 is cooled to a temperature of about4° C. The coolant line 12 is designed as an evaporator in the area ofcontainer 11. A condenser is provided outside the container. Thesecomponents are connected to form a cooling circuit in the manner knownper se via a throttling site and a compressor. The water condensed atthe evaporator 12 collects at the bottom of container 11.

The gas leaving the first thermal separation stage 10 enters via a line13 a second thermal separation stage 14 via a line 13. The secondthermal separation stage 14 is provided with two containers 15 withprovided as evaporators 16 in the form of coolant lines arranged in thetwo containers 15. The coolant lines of the evaporators 16 have the samedesign as described for the first thermal separation stage 10 and areconnected to a condenser. The cooling circuits have a compressor and acondenser each for all evaporators 16 together and a throttling site andare intended for alternating operation. The separation stages 10 and 14may be advantageously fed via a common cooling circuit, so that only onecompressor is necessary, and the different temperatures are set each bymeans of the associated throttling sites.

The hydrogen with the residual water still being entrained with it iscooled to −36° C. in this second thermal separation stage 14. Theremaining residual water resublimes or solidifies now on the evaporator16. The hydrogen leaving the second thermal separation stage 14 isavailable at the hydrogen removal port 17 and is dry, i.e., practicallywater-free. The containers 15 can be operating alternatingly viaoutlet-side valves 18, i.e., one of the containers is used for coolingwhile the other container is thawed and the water collecting at thebottom of the container is sent into the gravitational water separator 8via a line 20, which can likewise be shut off by means of a valve 19.Valve 19 in a return line 20 is opened only briefly each time, and valve18 belonging to the container 15 on the outlet side is actuated forshutting off until the thawed water is returned from container 15 intothe gravitational water separator 8.

A corresponding means is provided for container 11, and the water can betransferred from container 11 into the gravitational water separator 8via the line 21 connected there on the bottom side and the downstreamshut-off valve 22. The gravitational water separator 8 is to be bypassedfor this via a bypass line 23 and to be shut off by means of the valves24 and 25, so that after opening a valve 26 in bypass line 23, pressureis admitted to container 11 and the water present on the bottom ispressed via line 21 into the gravitational water separator 8. As analternative, this return line may also open directly into water tank 5.

A water return line 27, which can be connected to water tank 5 via avalve 28, adjoins the bottom of the gravitational water separator 8 inthis exemplary embodiment. The water separated in the water separationdevice 7 is consequently returned completely into the water tank 5. Theapparatus is typically operated such that the hydrogen is available witha pressure of 20-30 bar on the outlet side of the electrolyzer. Theelectrolyzer is operated now at a temperature between 70° C. and 80° C.

While specific embodiments of the invention have been shown anddescribed in detail to illustrate the application of the principles ofthe invention, it will be understood that the invention may be embodiedotherwise without departing from such principles.

1. An apparatus for the electrical production of hydrogen from water,the apparatus comprising: an electrolyzer of the PEM type, which has aninlet for introducing water and a first outlet for the hydrogen enrichedwith water and/or water vapor and produced in the electrolyzer, as wellas a second outlet for oxygen and water; and a water separation devicewith an inlet connected to the first outlet of the electrolyzer by meansof a line and with a gas-carrying outlet leading to a hydrogen removalport in or at the apparatus, wherein the water separation devicecomprises a thermal separation stage.
 2. An apparatus in accordance withclaim 1, wherein the water separation stage further comprises a secondseparation stage wherein the thermal separation stage is followed by thesecond separation stage.
 3. An apparatus in accordance with claim 2,wherein the second separation stage is also a thermal separation stagesuch that there are first and second thermal separation stages.
 4. Anapparatus in accordance with claim 3, further comprising a commoncooling circuit wherein the first and second thermal separation stagesare connected to the common cooling circuit.
 5. An apparatus inaccordance with claim 2, wherein the second separation stage has apressure swing adsorption apparatus.
 6. An apparatus in accordance withclaim 1, further comprising a mechanical preseparator between the firstoutlet of the electrolyzer and the inlet of the thermal separationstage.
 7. An apparatus in accordance with claim 6, wherein the waterseparated in the separation stage is introduced into the preseparatorvia return lines.
 8. An apparatus in accordance with claim 7, whereinthe return lines are provided with shut-off valves and a bypass line,which bypasses the preseparator and can be shut off by means of a valve,and wherein gas-carrying inlet and outlet lines of the preseparator canbe shut off by means of valves.
 9. An apparatus in accordance with claim7, wherein the preseparator is connected to the inlet for introducingwater by means of a line in the form of a return line that can be shutoff by means of a valve.
 10. An apparatus in accordance with claim 1,wherein the water separation device has a water-carrying outlet of atleast the first separation stage, which said outlet is connected to theinlet of the electrolyzer for returning the water by means of a line atleast from time to time.
 11. An apparatus in accordance with claim 1,wherein the thermal separation stage has an electrically operatedcooling apparatus.
 12. An apparatus in accordance with claim 11, whereinthe cooling apparatus comprises an absorber cooling apparatus, acompressor cooling apparatus or a cooling apparatus operated withPeltier elements.
 13. An apparatus in accordance with claim 1, whereinthe separation stage is designed such that hydrogen arriving from theelectrolyzer and enriched with water and/or hydrogen is cooled to atemperature below 5° C. and above the freezing point.
 14. An apparatusin accordance with claim 2, wherein the second separation stage is athermal separation stage, which is designed such that the hydrogendischarged from the first separation stage and enriched with waterand/or water vapor is cooled to below 0° C.
 15. An apparatus inaccordance with claim 2, wherein the second separation stage is athermal separation stage and is operated intermittently.
 16. Anapparatus in accordance with claim 1, wherein hydrogen that is producedis maintained under a pressure of 20 bar or more.
 17. An electricalhydrogen from water production apparatus comprising: a polymerelectrolyte membrane electrolyzer comprising an electrolyzer body withan electrolyzer inlet for introducing water, an electrolyzer firstoutlet for hydrogen enriched with water and/or water vapor and a secondelectrolyzer outlet for oxygen and water; an electrolyzer outlet line;and a water separator with a separator inlet connected to theelectrolyzer first outlet via said electrolyzer outlet line and with agas-carrying outlet leading to a hydrogen removal port, the waterseparator comprising a thermal separation stage.
 18. An apparatus inaccordance with claim 17, wherein said water separator further comprisesanother separation stage wherein the thermal separation stage isfollowed by the another separation stage.
 19. An apparatus in accordancewith claim 18, wherein the another separation stage is also a thermalseparation stage such that there are first and second thermal separationstages.
 20. An apparatus in accordance with claim 19, further comprisinga cooling apparatus cooling the first and second thermal separationstages.